There is significant current interest in the development of optical metamaterials for various applications including the processing and control of optical signals in the infrared spectrum. Metamaterial devices intended for such applications would be particularly desirable if the pertinent optical properties of the metamaterials could be actively tuned.
It has previously been shown that electrical control can be used to actively tune mid-infrared resonant frequencies of metallic split-ring resonators (SRRs) by altering carrier concentrations in an underlying semiconductor layer having an appropriate doping level. In that work, SRR arrays operated as an optical metamaterial layer and electrical metal gate simultaneously. With a reverse bias applied to the metal gate, the refractive index of the substrate directly underneath the metallic resonators was varied through changes in the depletion width in the highly doped semiconductor layer.
There is a need for further development of these, and similar ideas, leading to metamaterial-based optical devices exhibiting stronger tuning effects and operating in a broader range of optical frequencies.